A civilian has been killed and two guardsmen wounded in a suicide car bombing 180km north of the Iraqi capital, Baghdad.
Iraqi police said the car blew up at an Iraqi National Guard checkpoint west of the town of Baiji.
The town has seen frequent attacks by insurgents on US-led troops and Iraqi security forces.
Elsewhere, insurgents have fired a mortar barrage into the centre of Baghdad, killing one person and injuring 11.
Most of the casualties were caused by a mortar that exploded outside the offices of a mobile phone company.
Other mortars landed inside the Green Zone, the fortified compound that houses the interim Iraqi government.
In a separate development, the US military has said it will increase troop numbers in Iraq to 150,000 this month, the highest level since the war began in March last year.
The Pentagon said the decision had been taken to improve security in advance of next month's elections.
The decision means more than 10,000 personnel will have their tours of duty extended by two months.
